1. Field of the Invention
The present invention relates to a method of recording servo data on a high-density data recording medium, and more particularly, to a method of recording servo data on a hard disc on which high-density data can be recorded.
2. Description of the Related Art
Conventional methods of moving an actuator head in a hard disc drive (HDD) include a method using a stepping motor and a method using a voice coil motor.
The method using a stepping motor is usually used in a floppy disc drive (FDD) and is a method of moving a head in separated increments between tracks through a stepping motor.
Unlike in the method using a stepping motor, the method using a voice coil motor is a method of moving a head according to a special signal called a servo signal on a platter.
In a general hard disc, the entire surface of the platter is used to process the servo signal, and the hard disc has an extra head to read the servo signal. This case is referred to as a method using only a servo signal.
A more conventional method is a servo-signal insertion method. In the servo-signal insertion method, a servo signal is considered as one data and stored on a part of the surface of a platter. Accordingly, in the servo-signal insertion method, all platters in a hard disc drive system may be used for data storage. Thus, a head to read/write data in the servo-signal insertion method must read a servo signal.
In the method using a voice coil motor, a head can access a platter more accurately than that of the method using a stepping motor, and the head access time can be also reduced. In particular, in the servo-signal insertion method, an off-track can be modified in real-time, the surface of a hard disc can be used for various applications, and there is no interference between a servo head and a data head.
The servo signal in the method using a voice coil motor is obtained from servo data, which is recorded on a platter. The servo data includes patterns related to track data that are engraved when the HDD is manufactured on the surface of the platter to check the position of the head. In this case, the servo data is recorded on the surface of the platter while the head is rotated at a predetermined angle.
However, when the servo data is recorded on a hard disc using a voice coil motor, an angle that is formed by an extension line of a head actuator and a normal line of a track is varied according to a skew angle. That is, the skew angle is varied in accordance with regions in the direction of a radius of the hard disc on which servo data is recorded. In addition, the track density in an outer data region (hereinafter, referred to as an OD region) in the circumference of the hard disc is relatively higher than other regions of the hard disc. For example, the recording density in a position where the skew angle is 0 is about 57,000 tracks per inch (TPI), whereas the recording density in the OD region is about 60,000 TPI.
Under these circumstances, when the servo data is recorded on a hard disc through conventional methods of recording servo data, several problems occur as follows. When the servo data is recorded in a region where the skew angle of the hard disc is relatively large, for example, the OD region, servo bursts overlap. Specifically, when the servo data is recorded in a region where the skew angle of the hard disc is 0, for example, an inner data region (hereinafter, referred to as an ID region) of the hard disc, overlap does not occur between servo bursts B1 and B2 that are recorded in servo burst regions A and B of adjacent tracks, as illustrated in FIG. 1. However, when the servo data is recorded in the OD region of the hard disc, servo bursts B3 and B4 that are recorded in the servo burst regions A and B of the adjacent tracks overlap, as illustrated in FIG. 2. In this case, the absolute value of a position error signal (PES), which is used for position control by the servo control, becomes relatively small, and thus, the possibility of determining an off-track decreases.
That is, in the case of an on-track, as shown in Equations 1 and 2, the value of the PES is 0 in either case.
                    PES        =                                            (                              A                -                B                            )                                      (                              A                +                B                            )                                =                                                    (                                                      0.4                    ⁢                    T                                    -                                      0.4                    ⁢                    T                                                  )                                            (                                                      0.4                    ⁢                    T                                    +                                      0.4                    ⁢                    T                                                  )                                      =            0                                              (        1        )                                PES        =                                            A              +              d              -              B              -              d                                      A              +              d              +              B              +              d                                =                                                    (                                                      0.4                    ⁢                    T                                    +                                      0.1                    ⁢                    T                                    -                                      0.4                    ⁢                    T                                    -                                      0.1                    ⁢                    T                                                  )                                            (                                                      0.4                    ⁢                    T                                    +                                      0.1                    ⁢                    T                                    +                                      0.4                    ⁢                    T                                    +                                      0.1                    ⁢                    T                                                  )                                      =            0                                              (        2        )            
Meanwhile, when an off-track of 10% exists, as shown in Equation 3, the value of the PES is 0.25 when the servo bursts are normally recorded on the adjacent tracks. However, as shown in Equation 4, the value of the PES is 0.20 when the servo bursts overlap.
                              PES          ⁡                      (                          off              -                              track                ⁢                                                                  ⁢                10                ⁢                %                                      )                          =                                            (                              A                +                                  0.1                  ⁢                  T                                -                B                +                                  0.1                  ⁢                  T                                            )                                      (                              A                +                                  0.1                  ⁢                  T                                +                B                -                                  0.1                  ⁢                  T                                            )                                =                                                    0.2                ⁢                T                                            0.8                ⁢                T                                      =            0.25                                              (        3        )                                          PES          ⁡                      (                          off              -                              track                ⁢                                                                  ⁢                10                ⁢                %                                      )                          =                                            (                              A                +                                  0.1                  ⁢                  T                                +                                  0.1                  ⁢                  T                                -                B                -                                  0.1                  ⁢                  T                                +                                  0.1                  ⁢                  T                                            )                                      (                              A                +                                  0.1                  ⁢                  T                                +                                  0.1                  ⁢                  T                                +                B                +                                  0.1                  ⁢                  T                                -                                  0.1                  ⁢                  T                                            )                                =                                                    0.2                ⁢                T                                            1.0                ⁢                T                                      =            0.2                                              (        4        )            
The values of the servo bursts in the regions A and B as shown in Equations 1 through 4 are 0.4T, and a value d by which the servo bursts deviate from a servo burst space D1 in the region where the servo bursts overlap is 0.1 T.
In this way, the value of the PES in the region where the servo bursts overlap cannot represent an off-track which actually occurs, resulting in defects when the data is recorded on the hard disc, or when the data is read from the hard disc.